[gitignore] ignore config files for lightcnn

2 jobs for add-lightCNN29 in 9 minutes and 33 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #156015
docker
build_linux_36

00:09:30

71.0%
passed #156016
macosx
build_macosx_36

00:01:48